The present invention relates to the monitoring of substances entrained or dissolved in a liquid. More particularly, the invention provides a continuous tape carrying many test stations for sequential repetitive testing of samples of a liquid, typically water, taken from a swimming pool or reservoir where the substance in said liquid may either be desirable, for example chlorine in a swimming pool, or undesirable, for example an excess of sulfates, chlorides, nitrates and magnesium in a reservoir supplying drinking water.
The present specification deals primarily with chemical indicator strips, as opposed to thermal and stress indicator strips. Indicator strips are a known and used tool for determining if a chemical is present in a defined space or in a liquid of interest. The tape is exposed to the substance to be tested, and the color changes seen in the tape are indicative that such chemical is or is not present above a predefined level. For example, a strip used to monitor a reservoir holding drinking water could indicate whether the water contains the desired level of fluoride, and/or whether the water is within a defined range for the pH value.
Indicator strips are usually supplied in short lengths, and testing is carried out manually. Manual testing is suitable for applications where testing needs to be carried out only once or twice a day. However due to government or municipality regulations it is sometimes required to carry out frequent tests and in some situations even to provide proof that such tests were carried out and that the test results indicate that the substance of interest was present within an allowed concentration range. When many sequential tests are needed, manual test execution is tiresome and unreliable, and automatic testing is the best option.
The state of the art regarding indicator strips can be surmised from a review of recent US patents.
In U.S. Pat. No. 5,841,896 Tsuchiya discloses an apparatus for displaying the hue of a signal by using an indicator strip carrying printed indicia to indicate various hues.
Markart proposes a discrete test card in U.S. Pat. No. 6,027,689, useful primarily in the testing of body fluids. The card can be divided into individual test sections.
The indicator strip proposed by Barclay in U.S. Pat. No. 6,322,750 is responsive to gases, particularly hydrogen sulfide.
Cole discloses a multi-level semi-quantitative immunodiffusion assay in U.S. Pat. No. 6,656,745. While used for analysis, the device is not in the form of a tape.
A color-based system for automatic continuous effluent analysis is described by McNab, Incorporated, on the company's web site. However the system does not employ a continuous indicator tape.
For repetitive tests manual methods using discrete pieces of indicator tape are laborious and inconvenient, particularly when testing is required at fixed times around the clock.
It is therefore one of the objects of the present invention to obviate the disadvantages of prior art indicator tapes and arrangements for their deployment and to provide a testing system for liquids which is automatic and suitable for executing frequent tests.